1. Field of the Invention
The present invention relates to a prosthesis of generally tubular shape for controlling the direction of flow in a duct of a living organism, this prosthesis being made of a biocompatible, elastically deformable material and comprising an annular proximal fixing part in a section of greater diameter of said duct, and a distal part whose wall is dimensioned to allow it to collapse on itself in the presence of an overpressure exerted on its outer surface, and also relates to a method for fitting this prosthesis.
2. Description of the Prior Art
Such prostheses have in particular been proposed for controlling gastric reflux into the esophagus in persons suffering generally from a hiatal hernia accompanied by reflux esophagitis. This repeated reflux of gastric acid attacks the wall of the esophagus and eventually leads to esophagitis which is manifested by ulceration of the wall and sometimes by a narrowing of its cross section. It has been proposed, particularly in WO 96/29954, to provide a prosthesis intended to permit the flow of food from the esophagus to the stomach but to stop the reflux of the gastric content from the stomach into the esophagus under the reflux pressure by means of folding in and/or xe2x80x9ccollapsingxe2x80x9d. The problem with such prostheses lies in how they are fixed and in how they are changed, in other words their fitting and removal. In fact, as this condition is a chronic one, a patient will have to be equipped with such a prosthesis on a continuous basis, so that the latter will need to be changed periodically, especially as a result of the aging of the materials used, generally elastomers, and the particularly aggressive conditions of the environment in which it is located, the gastric acid having a pH of the order of 1. The only solutions proposed however are either surgical or involve fastening elements of an unspecified nature. The surgical route would only really be acceptable if the prosthesis could be guaranteed for the lifetime of the patient. However, it is well known that all elastomers age and that the environment in which the prosthesis is intended to function is also particularly aggressive, so that the surgical route does not represent a solution because it would have to be performed periodically, whereas there are other drug-based therapeutic routes including antacids which tend to render the environment neutral, H2 antihistamines which fix to the H2 receptors of the parietal cell, and medicines which block the production of H+ ions by the parietal cell. A common feature of these medicines is that they do not cure the illness from which the patient is suffering, with the result that they have to be administered continuously. It is clear at present that none of the solutions proposed is satisfactory, given that they only offer a choice between continuous administration of medicines and repeated surgical interventions.
It is clear that the prosthesis constitutes without doubt the best potential solution in that it allows the dysfunction from which the patient is suffering to be remedied by purely mechanical means. However, this solution only becomes feasible if the fitting and removal of this prosthesis can be done by the endoscopic route.
It is precisely the object of the present invention to propose a solution which permits fitting and removal of the prosthesis by the endoscopic route.
To this end, the present invention relates to a prosthesis of generally tubular shape for controlling the direction of flow in a duct of a living organism, this prosthesis being made of a biocompatible, elastically deformable material and comprising an annular proximal fixing part in a section of greater diameter of said duct, and a distal part whose wall is dimensioned to allow it to collapse on itself in the presence of an overpressure exerted on its outer surface, characterized in that said annular proximal fixing part is associated over a certain width with stiffening means for giving it a resistance to crushing which is greater than that of the distal part of the prosthesis, able to retain the prosthesis by applying said annular proximal part against the wall of said section of greater diameter of said duct with a force sufficient to ensure that it is held in place as the food bolus passes through it.
The present invention also relates to a method for fitting this prosthesis wherein the temperature of the element made of shape-memory alloy is first lowered at least to its lower temperature limit of its temperature range of martensitic transformation, the diameter of said prosthesis is then reduced to allow it to be placed in a hiatal hernia, the element made of shape-memory alloy is freed from its constraint and it is heated until its temperature reaches at least the upper limit of its austenitic transformation temperature and it recovers its initial shape.
It is precisely the object of the present invention to propose a solution which permits fitting and removal of the prosthesis by the endoscopic route.
To this end, the present invention relates to a prosthesis of generally tubular shape as claimed in claim 1 and to a method for fitting this prosthesis as claimed in claim 12.